Hydrotreating of guaiacol: A comparative study of Red mud-supported nickel and commercial Ni/SiO2-Al2O3 catalysts

Abstract

Upgrading of bio-oil through catalytic hydrotreating was investigated with guaiacol as a model compound. A nickel supported on red mud (Ni/RM) hydrotreating catalyst was developed and compared to the standard Ni/SiO2-Al2O3 catalysts under similar experimental conditions. The Ni/RM catalyst was characterized by inductively coupled plasma atomic emission spectrometry (ICP-AES), X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), BET specific surface area, and temperature programmed reduction (TPR). The effects of reaction temperature (300, 350, 400 °C) and initial hydrogen pressure (4.83 MPa (700 psi), 5.52 MPa (800 psi), and 6.21 MPa (900 psi)) on products distribution were investigated. The major products of hydrotreating process were catechol, anisole, phenol, cyclohexane, hexane, benzene, toluene, and xylene. Increasing the reaction temperature and hydrogen pressure improved HDO reactions. Complete HDO was achieved at reaction temperature of 400 °C and initial hydrogen pressure of 6.21 MPa (900 psi). Under these conditions, the selectivity to cyclohexane, benzene, toluene, and xylene over Ni/RM catalyst were 38.8, 24.5, 18.1, and 7.9% respectively, whereas these values were 62.2, 15.9, 8.4, and 4.5% respectively over Ni/SiO2-Al2O3. Reaction network and the kinetics of guaiacol HDO were proposed according to analysis of the products. The Ni/RM catalyst was more effective for deoxygenation reactions than hydrogenation while commercial Ni/SiO2-Al2O3 was more effective for hydrogenation than deoxygenation. Thus, hydrogen consumption per gram of bio-oil was lower for the Ni/RM catalyst compared to the Ni/SiO2-Al2O3. There was less hydrocracking and coke formation for the Ni/RM compared to the commercial catalyst and this resulted in higher liquid yield for the new catalyst.